Recently, digital terrestrial broadcasting using an OFDM modulation method has been started.
However, the reception system of a portable terminal receives broadcasting using a small antenna. Thus, the small antenna must receive signals in a lower position from the ground surface than a large household antenna in a fixed reception system for household use. In addition, because the user of the portable terminal receives broadcasting while moving, the reception environment is drastically degraded in the reception system of the portable terminal. In particular, it is necessary to restore the signal waveforms at transmission from the signal waveforms received in a poor reception environment that includes frequency-selective channel distortions resulting from multipath and fading resulting from moving reception, and to reproduce the broadcasted programs.
Conventionally, it has been known that a channel correction technology is effective in such a poor reception environment.
The channel correction technology estimates the waveform distortions produced in a channel and eliminates the distortions in reception signals, for correction. In the digital broadcasting, pilot signals known by both transmission and reception sides are arranged at predetermined intervals in the frequency-axis direction and in the time-axis direction. Thus, a reception device calculates changes in amplitude and the amount of phase rotation from the differences between the pilot signals received and the pilot signals generated inside of the receiver, to clarify the waveform distortions and time variations produced in the channel. Therefore, interpolation based on this information allows estimation and correction of the waveform distortions and time variations in the data signal positions other than the pilot signals, thus improving multipath tolerance and fading tolerance.
For example, Non-Patent Document 1 is known as the information on a conventional art of the present invention.
In the channel estimation using pilot signals, the reception characteristics greatly vary with the positions of the pilot signals to be used for estimation. For example, between a channel estimation using pilot signals spaced at first intervals in the time-axis direction (symbol direction) and a channel estimation using pilot signals spaced at second intervals shorter than the first intervals, the accuracy of estimating time variations and frequency-selective distortions in the reception signal is different. Such a difference varies the multipath tolerance and fading tolerance of the OFDM reception device.
Conventionally, either one of these channel estimation techniques has been used for interpolation. Thus, achievement of both multipath tolerance and fading tolerance at the same time has been difficult.    [Non-patent Document 1] Noritaka Iguchi, Ryosuke Mori, Akira Kisoda, and Ippei Kanno, “Channel Estimation using Diagonal Interpolation in Digital Terrestrial Broadcasting Receiver”, The Institute of Electronics, Information, and Communication Engineers Conference Collected Papers, vol. 2005, Society 1, 531 pp